Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$114.84	12.139%	$128.7804	$128.78	$128.80	$128.80
Purchase #2	$85.60	4.114%	$89.1216	$89.12	$89.10	$89.10
Purchase #3	$86.75	5.521%	$91.5395	$91.54	$91.55	$91.50
Purchase #4	$16.46	5.501%	$17.3655	$17.37	$17.35	$17.40
Purchase #5	$42.37	11.857%	$47.3938	$47.39	$47.40	$47.40
Purchase #6	$38.88	13.760%	$44.2299	$44.23	$44.25	$44.20
Purchase #7	$239.96	3.184%	$247.6003	$247.60	$247.60	$247.60
7 purchase totals =	$624.86		$666.0310	$666.03	$666.05	$666.00